The Experts below are selected from a list of 291 Experts worldwide ranked by ideXlab platform
Alessandro Gomez - One of the best experts on this subject based on the ideXlab platform.
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chemical interactions between 1 2 4 trimethylbenzene and n decane in doped counterflow Gaseous Diffusion flames
Proceedings of the Combustion Institute, 2015Co-Authors: Francesco Carbone, Alessandro GomezAbstract:Abstract The chemical interaction of the two-components of a jet fuel surrogate, n -decane and 1,2,4-trimethylbenzene (TMB), was studied by adding several hundreds ppm of each chemical to two counterflow Diffusion flames, one using methane and the other ethylene as baseline fuels. The objective was to look into evidence of synergistic effects due to the interaction of these reference fuels, that are representative of normal alkanes and aromatics, respectively, making up the bulk of practical fuels. The dopants were added in the same proportions as in the Aachen surrogate of jet fuel. The flames presented two distinct environments: the permanently blue methane flame and the incipiently sooting ethylene flame provide well defined temperature–time histories and chemical environments, with the one based on ethylene being relatively more oxygen-deficient. Profiles of critical pyrolysis products and of some stable soot precursors were determined from GC/MS analysis of gas samples extracted from the flames and compared with results from the OPPDIFF model using a lumped chemical mechanism. Mechanistically relevant synergies among the two fuel components are highlighted considering the production rate of aromatics in both flames when adding the two components either simultaneously or separately. The principal observation is that the combined addition of the two components causes an overproduction of methane in the ethylene flame, a decrease in the concentration of acetylene in the methane flame and an acceleration of the aromatic destruction/growth pathways. The model for the most part fails to capture the principal evidence of synergistic effects. Most of the other quantified species reveal no synergy, their concentration being the sum of the contributions of each component used individually, partly because of the small amounts of reactants that were added to the flames.
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experimental study on the structure of opposed flow Gaseous Diffusion flames doped with n decane
Combustion and Flame, 2014Co-Authors: Francesco Carbone, Alessandro GomezAbstract:Abstract The destruction of n -decane is investigated with a perturbative approach by adding hundreds of ppm to the fuel stream of two Gaseous counterflow Diffusion flames at atmospheric pressure: a blue methane flame and an incipiently sooting ethylene flame that offer distinct reacting environments. The detailed chemical structure of the flames including the products of n -decane consumption is determined using a microprobe gas sampling technique followed by GC/MS analysis. Experimentally, principal products of n -decane destruction are C2–C9 linear alpha-olefins that are found at ever increasing concentrations with decreasing carbon number, starting with 1-nonene all the way to propene and ethylene, the most abundant products. Successive fragmentation steps of the n -decane primary products lead to the formation of C2–C5 dienes and other hydrocarbons with multiple unsaturated bonds. The consumption rate of n -decane is more abrupt in the methane flame as compared to the gentler decay observed in the ethylene flame. The addition of n -decane in the ethylene flame does not contribute to the formation of soot precursors such as aromatic compounds because the pool of C2–C4 fragments of the baseline flame, playing a key role in aromatic growth, is only marginally affected by n -decane addition. The comprehensive database of stable species of the experimental component of the study is tested by a comparison with the results of modeling the flames using two semi-detailed chemical kinetic mechanisms, Ranzi-mech and JetSurF. Shortcomings of these mechanisms are highlighted for different classes of compounds by comparison of the model results with the experimental data leaving room for future improvements in their formulation.
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chemical effects of 1 2 4 trimethyl benzene addition in counterflow Gaseous Diffusion flames
Proceedings of the Combustion Institute, 2013Co-Authors: Francesco Carbone, Alessandro GomezAbstract:Abstract The structure of Gaseous counterflow Diffusion flames perturbed with the addition of hundreds of ppm of prevaporized 1,2,4-trimethyl benzene (TMB) is studied in two distinct flame environments: a blue methane flame and an incipiently sooting ethylene flame. The two flames provide well defined temperature-time histories and chemical environments to investigate the behavior of complex fuels and complement other reacting environments lacking the coupling of kinetics and transport that is typical of flame environments. Profiles of critical pyrolysis products and of some stable soot precursors are determined from GC/MS analysis of gas samples extracted from the flames and compared with results from the OPPDIFF model using a semi-detailed chemical mechanism. Experimentally, because of the presence of aliphatic fragments, TMB reactivity is enhanced in these flames with the onset of TMB decay beginning at relatively modest temperatures, on the order of 800 K. The dominant path to stable species is driven by H radical attack. It leads in sequence to xylenes, toluene (through benzyl radical) and benzene formation. This enhanced reactivity is captured reasonably well by the model in the methane flame, but not in the ethylene flame, in the presence of a richer, more complex mixture. The model does not reproduce accurately the pathway yielding C3 and some C4 species from TMB cracking. Aromatic ring opening is the bottleneck in the TMB cracking process in the methane flame but not in the ethylene one. Indene, an important soot precursor for monoaromatic fuels since the second aromatic ring formation is considered to be a bottleneck in the process, is measured in the ethylene flame in poor agreement with the model predictions. The dataset presented here and available supplemental data online may help identifying improvements to the chemical kinetic mechanism of this reference fuel.
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the structure of toluene doped counterflow Gaseous Diffusion flames
Combustion and Flame, 2012Co-Authors: Francesco Carbone, Alessandro GomezAbstract:Abstract The structure of Gaseous counterflow Diffusion flames perturbed with the addition of hundreds of ppm of prevaporized toluene is studied in two distinct flame environments: a blue methane flame stabilized on the fuel side of the gas stagnation plane and an incipiently sooting ethylene flame stabilized on the oxidizer side. The goal is to provide a well-defined testbed in terms of temperature–time history, major species and part of the radical pool, for the examination of reference fuels that are critical components of practical fuel blends. Gas samples are extracted from the flame with fused silica microprobes for subsequent GC/MS analysis and thermocouples and thin filament pyrometry are used to characterize the temperature field. Profiles of critical toluene pyrolysis products and stable soot precursors are compared with computational models using two semi-detailed chemical mechanisms. Results show that in the methane flame some oxygen containing radicals like O and OH are contributing early on to the toluene destruction path. In the incipiently sooting ethylene flame, the primary attack is from H alone. This finding confirms the different challenges that such flames pose to the validation of a chemical kinetic mechanism. The onset of toluene decay in these flames begins at relatively modest temperatures, on the order of 800 K. This reactivity is captured reasonably well by both chemical mechanisms in the methane flame, in the absence of reactants larger than C2, but not so in the ethylene flame, in the presence of a richer, more complex mixture. The aromatic ring opening mechanisms are not adequately modeled in either case. This discrepancy has implications for the modeling of practically relevant fuel blends with both aliphatic and aromatic compounds. The dominant species larger than toluene in the doped methane flame is ethylbenzene, which at least one of the mechanisms reproduces quite well. The largest measured species in the incipiently sooting flame is indene, whose concentration increase due to toluene addition is properly captured by one of the models. The experimental dataset reported here may help identifying future improvements to chemical kinetic mechanisms and complement other reactor datasets lacking the coupling of kinetics and transport of flame environments.
Francesco Carbone - One of the best experts on this subject based on the ideXlab platform.
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chemical interactions between 1 2 4 trimethylbenzene and n decane in doped counterflow Gaseous Diffusion flames
Proceedings of the Combustion Institute, 2015Co-Authors: Francesco Carbone, Alessandro GomezAbstract:Abstract The chemical interaction of the two-components of a jet fuel surrogate, n -decane and 1,2,4-trimethylbenzene (TMB), was studied by adding several hundreds ppm of each chemical to two counterflow Diffusion flames, one using methane and the other ethylene as baseline fuels. The objective was to look into evidence of synergistic effects due to the interaction of these reference fuels, that are representative of normal alkanes and aromatics, respectively, making up the bulk of practical fuels. The dopants were added in the same proportions as in the Aachen surrogate of jet fuel. The flames presented two distinct environments: the permanently blue methane flame and the incipiently sooting ethylene flame provide well defined temperature–time histories and chemical environments, with the one based on ethylene being relatively more oxygen-deficient. Profiles of critical pyrolysis products and of some stable soot precursors were determined from GC/MS analysis of gas samples extracted from the flames and compared with results from the OPPDIFF model using a lumped chemical mechanism. Mechanistically relevant synergies among the two fuel components are highlighted considering the production rate of aromatics in both flames when adding the two components either simultaneously or separately. The principal observation is that the combined addition of the two components causes an overproduction of methane in the ethylene flame, a decrease in the concentration of acetylene in the methane flame and an acceleration of the aromatic destruction/growth pathways. The model for the most part fails to capture the principal evidence of synergistic effects. Most of the other quantified species reveal no synergy, their concentration being the sum of the contributions of each component used individually, partly because of the small amounts of reactants that were added to the flames.
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experimental study on the structure of opposed flow Gaseous Diffusion flames doped with n decane
Combustion and Flame, 2014Co-Authors: Francesco Carbone, Alessandro GomezAbstract:Abstract The destruction of n -decane is investigated with a perturbative approach by adding hundreds of ppm to the fuel stream of two Gaseous counterflow Diffusion flames at atmospheric pressure: a blue methane flame and an incipiently sooting ethylene flame that offer distinct reacting environments. The detailed chemical structure of the flames including the products of n -decane consumption is determined using a microprobe gas sampling technique followed by GC/MS analysis. Experimentally, principal products of n -decane destruction are C2–C9 linear alpha-olefins that are found at ever increasing concentrations with decreasing carbon number, starting with 1-nonene all the way to propene and ethylene, the most abundant products. Successive fragmentation steps of the n -decane primary products lead to the formation of C2–C5 dienes and other hydrocarbons with multiple unsaturated bonds. The consumption rate of n -decane is more abrupt in the methane flame as compared to the gentler decay observed in the ethylene flame. The addition of n -decane in the ethylene flame does not contribute to the formation of soot precursors such as aromatic compounds because the pool of C2–C4 fragments of the baseline flame, playing a key role in aromatic growth, is only marginally affected by n -decane addition. The comprehensive database of stable species of the experimental component of the study is tested by a comparison with the results of modeling the flames using two semi-detailed chemical kinetic mechanisms, Ranzi-mech and JetSurF. Shortcomings of these mechanisms are highlighted for different classes of compounds by comparison of the model results with the experimental data leaving room for future improvements in their formulation.
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chemical effects of 1 2 4 trimethyl benzene addition in counterflow Gaseous Diffusion flames
Proceedings of the Combustion Institute, 2013Co-Authors: Francesco Carbone, Alessandro GomezAbstract:Abstract The structure of Gaseous counterflow Diffusion flames perturbed with the addition of hundreds of ppm of prevaporized 1,2,4-trimethyl benzene (TMB) is studied in two distinct flame environments: a blue methane flame and an incipiently sooting ethylene flame. The two flames provide well defined temperature-time histories and chemical environments to investigate the behavior of complex fuels and complement other reacting environments lacking the coupling of kinetics and transport that is typical of flame environments. Profiles of critical pyrolysis products and of some stable soot precursors are determined from GC/MS analysis of gas samples extracted from the flames and compared with results from the OPPDIFF model using a semi-detailed chemical mechanism. Experimentally, because of the presence of aliphatic fragments, TMB reactivity is enhanced in these flames with the onset of TMB decay beginning at relatively modest temperatures, on the order of 800 K. The dominant path to stable species is driven by H radical attack. It leads in sequence to xylenes, toluene (through benzyl radical) and benzene formation. This enhanced reactivity is captured reasonably well by the model in the methane flame, but not in the ethylene flame, in the presence of a richer, more complex mixture. The model does not reproduce accurately the pathway yielding C3 and some C4 species from TMB cracking. Aromatic ring opening is the bottleneck in the TMB cracking process in the methane flame but not in the ethylene one. Indene, an important soot precursor for monoaromatic fuels since the second aromatic ring formation is considered to be a bottleneck in the process, is measured in the ethylene flame in poor agreement with the model predictions. The dataset presented here and available supplemental data online may help identifying improvements to the chemical kinetic mechanism of this reference fuel.
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the structure of toluene doped counterflow Gaseous Diffusion flames
Combustion and Flame, 2012Co-Authors: Francesco Carbone, Alessandro GomezAbstract:Abstract The structure of Gaseous counterflow Diffusion flames perturbed with the addition of hundreds of ppm of prevaporized toluene is studied in two distinct flame environments: a blue methane flame stabilized on the fuel side of the gas stagnation plane and an incipiently sooting ethylene flame stabilized on the oxidizer side. The goal is to provide a well-defined testbed in terms of temperature–time history, major species and part of the radical pool, for the examination of reference fuels that are critical components of practical fuel blends. Gas samples are extracted from the flame with fused silica microprobes for subsequent GC/MS analysis and thermocouples and thin filament pyrometry are used to characterize the temperature field. Profiles of critical toluene pyrolysis products and stable soot precursors are compared with computational models using two semi-detailed chemical mechanisms. Results show that in the methane flame some oxygen containing radicals like O and OH are contributing early on to the toluene destruction path. In the incipiently sooting ethylene flame, the primary attack is from H alone. This finding confirms the different challenges that such flames pose to the validation of a chemical kinetic mechanism. The onset of toluene decay in these flames begins at relatively modest temperatures, on the order of 800 K. This reactivity is captured reasonably well by both chemical mechanisms in the methane flame, in the absence of reactants larger than C2, but not so in the ethylene flame, in the presence of a richer, more complex mixture. The aromatic ring opening mechanisms are not adequately modeled in either case. This discrepancy has implications for the modeling of practically relevant fuel blends with both aliphatic and aromatic compounds. The dominant species larger than toluene in the doped methane flame is ethylbenzene, which at least one of the mechanisms reproduces quite well. The largest measured species in the incipiently sooting flame is indene, whose concentration increase due to toluene addition is properly captured by one of the models. The experimental dataset reported here may help identifying future improvements to chemical kinetic mechanisms and complement other reactor datasets lacking the coupling of kinetics and transport of flame environments.
Long Zhang - One of the best experts on this subject based on the ideXlab platform.
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performance comparisons of desiccant wheels for air dehumidification and enthalpy recovery
Applied Thermal Engineering, 2002Co-Authors: Long Zhang, Jianlei NiuAbstract:Desiccant wheels have two major applications: air dehumidification and enthalpy recovery. Since the operating conditions are different, heat and mass transfer behaviors in the wheels are quite different. In this paper, the performances of desiccant wheels used in air dehumidification and enthalpy recovery are compared with each other. To accomplish this task, a two-dimensional, dual-Diffusion transient heat and mass transfer model which takes into account the heat conduction, the surface and Gaseous Diffusion in both the axial and the thickness directions is presented. Effects of the rotary speed, the number of transfer units, and the specific area on the performance of the wheel are investigated and compared in the two situations. The cycles that the desiccant and air undergo in the wheel are plotted in psychrometric charts to demonstrate the different heat and moisture transfer mechanisms during the dehumidification and enthalpy recovery processes.
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performance comparisons of desiccant wheels for air dehumidification and enthalpy recovery
Applied Thermal Engineering, 2002Co-Authors: Long ZhangAbstract:Desiccant wheels have two major applications: air dehumidification and enthalpy recovery. Since the operating conditions are different, heat and mass transfer behaviors in the wheels are quite different. In this paper, the performances of desiccant wheels used in air dehumidification and enthalpy recovery are compared with each other. To accomplish this task, a two-dimensional, dual-Diffusion transient heat and mass transfer model which takes into account the heat conduction, the surface and Gaseous Diffusion in both the axial and the thickness directions is presented. Effects of the rotary speed, the number of transfer units, and the specific area on the performance of the wheel are investigated and compared in the two situations. The cycles that the desiccant and air undergo in the wheel are plotted in psychrometric charts to demonstrate the different heat and moisture transfer mechanisms during the dehumidification and enthalpy recovery processes.
James L Smialek - One of the best experts on this subject based on the ideXlab platform.
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sic recession due to sio2 scale volatility under combustion conditions part 2 thermodynamics and Gaseous Diffusion model
2013Co-Authors: Elizabeth J Opila, Raymond C Robinson, James L Smialek, Dennis S Fox, Nathan S JacobsonAbstract:In combustion environments, volatilization of SiO2 to Si-O-H(g) species is a critical issue. Available thermochemical data for Si-O-H(g) species were used in the present study to calculate boundary-layer-controlled fluxes from SiO2. Calculated fluxes were compared to volatilization rates of SiO2 scales grown on SiC, which were measured in a high-pressure burner rig, as reported in Part I of this paper. Calculated volatilization rates also were compared to those measured in synthetic combustion gas furnace tests. Probable vapor species were identified in both fuel-lean and fuel-rich combustion environments, based on the observed pressure, temperature, and velocity dependencies, as well as on the magnitude of the volatility rate. Water vapor was responsible for the degradation of SiO2 in the fuel-lean environment. SiO2 volatility in fuel-lean combustion environments was attributed primarily to the formation of Si(OH)4(g), with a small contribution of SiO(OH)2(g). Reducing gases such as H2 and/or CO, in combination with water vapor, contributed to the degradation of SiO2 in the fuel-rich environment. The model to describe SiO2 volatility in a fuel-rich combustion environment gave a less satisfactory fit to the observed results. Nevertheless, it was concluded-given the known thermochemical data-that SiO2 volatility in a fuel-rich combustion environment is best described by the formation of SiO(g) at 1 atm total pressure and the formation of Si(OH)4(g), SiO(OH)2(g), and SiO(OH)(g) at higher pressures. Other Si-O-H(g) species, such as Si2(OH)6, may contribute to the volatility of SiO2 under fuel-rich conditions; however, complete thermochemical data are unavailable at this time.
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sic recession caused by sio2 scale volatility under combustion conditions i experimental results and empirical model
Journal of the American Ceramic Society, 1999Co-Authors: Raymond C Robinson, James L SmialekAbstract:A high-pressure burner rig was developed to evaluate the response of chemical-vapor-deposited SiC material during exposure to simulated gas turbine combustor conditions. Linear weight loss and surface recession rates of SiC were observed in both fuel-lean and fuel-rich gas mixtures. This response was shown to result from SiO2 scale volatility. Arrhenius-type temperature dependence was demonstrated. In addition, the effects of pressure and gas velocity were defined in terms of a Gaseous-Diffusion-controlled process for volatile reaction products (such as SiO, Si(OH)4, and iO(OH)x). Accordingly, multiple linear regression was used to develop empirical recession relationships of the form exp(-DeltaQ/RT)Pxvyfor both lean and rich combustion conditions. Part II of this paper discusses the thermodynamics and Gaseous-Diffusion model of this recession. The empirical models discussed here enable prediction of SiC recession for any combination of T, P, and vin turbine environments. For typical combustion conditions, recession of 0.2-2 µm/h was predicted at 1200°-1400°C. Thus, long-term, high-temperature, high-velocity exposure may degrade silicon-based or SiO2-forming material by recession in combustion gas environments.
Jessica Furrer Chau - One of the best experts on this subject based on the ideXlab platform.
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linking drainage front morphology with Gaseous Diffusion in unsaturated porous media a lattice boltzmann study
Physical Review E, 2006Co-Authors: Jessica Furrer ChauAbstract:The effect of drainage front morphology on Gaseous Diffusion through partially saturated porous media is analyzed using the lattice Boltzmann method (LBM). Flow regimes for immiscible displacement in porous media have been characterized as stable displacement, capillary fingering, and viscous fingering. The dominance of a flow regime is associated with the relative magnitudes of gravity, viscous, and capillary forces, quantifiable via the Bond number Bo, capillary number Ca, and their difference, Bo-Ca. Forced drainage from an initially saturated two-dimensional (2D) porous medium was simulated and the resulting flow patterns were analyzed and compared with theoretical predictions and experimental results. The LBM simulations reproduced expected flow morphologies for a range of drainage velocities and gravitational forces (i.e., a range of capillary and Bond numbers). Furthermore, measures of drainage front width as a function of the dimensionless difference Bo-Ca correspond well with scaling laws derived from percolation theory. Effects of flow morphology on residual fluid entrapment and Gaseous Diffusion were assessed by running LBM Diffusion simulations through the partially saturated domain for a range of water contents. The effective Diffusion coefficient as a function of water content was estimated for three regimes: stable drainage front, capillary fingering, and viscous fingering. Significant reductions in Gaseous Diffusion coefficient were found for viscous fingering relative to stable displacement, and to a lesser extent for capillary fingering, indicating that wetting phase distribution with a high degree of fingering in the 2D domain severely restricts connectivity of gas Diffusion pathways through the medium. The study lends support for the use of LBM in design and management of fluids in porous media under variable gravity, and enhances the understanding of the role of dynamic fluid behavior on macroscopic transport properties of partially saturated porous media.
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simulation of Gaseous Diffusion in partially saturated porous media under variable gravity with lattice boltzmann methods
Water Resources Research, 2005Co-Authors: Jessica Furrer Chau, Michael C SukopAbstract:Liquid distributions in unsaturated porous media under different gravitational accelerations and corresponding macroscopic Gaseous Diffusion coefficients were investigated to enhance understanding of plant growth conditions in microgravity. We used a single-component, multiphase lattice Boltzmann code to simulate liquid configurations in two-dimensional porous media at varying water contents for different gravity conditions and measured gas Diffusion through the media using a multicomponent lattice Boltzmann code. The relative Diffusion coefficients (D rel) for simulations with and without gravity as functions of air-filled porosity were in good agreement with measured data and established models. We found significant differences in liquid configuration in porous media, leading to reductions in D rel of up to 25% under zero gravity. The study highlights potential applications of the lattice Boltzmann method for rapid and cost-effective evaluation of alternative plant growth media designs under variable gravity.